为什么忽略我的默认/可选参数?
grid_model.h
void GridModel::PrintGrid(bool flag = false) {
// things...
}
grid_model.cpp
ns::GridModel* gm = new GridModel();
gm->PrintGrid(true); // works
gm->PrintGrid(); // doesn't work
grid_model_test.cpp
grid_model_test.cpp:22:12: error: no matching function for call to ‘ns::GridModel::PrintGrid()’
gm->PrintGrid();
^
In file included from grid_model_test.cpp:2:0:
grid_model.h:27:7: note: candidate: void ns::GridModel::PrintGrid(bool)
void PrintGrid(bool);
^~~~~~~~~
错误:
#include <iostream>
class Thing {
public:
void Whatever(bool);
};
void Thing::Whatever(bool flag = false) {
std::cout << "Parameter was: " << flag << std::endl;
}
int main() {
Thing* thing = new Thing();
thing->Whatever();
return 0;
}
当我在其他地方使用它们时,它们似乎工作正常。
ssh -o ConnectionAttempts=1 -o ConnectTimeout=10 user@IP exit
答案 0 :(得分:3)
作为良好的设计实践,默认参数值应放在声明中,而不是放在实现中:
class GridModel {
public:
GridModel();
void PrintGrid(bool flag=false);
};
void GridModel::PrintGrid(bool flag) {
// things...
}
从技术上讲(如此处http://en.cppreference.com/w/cpp/language/default_arguments更详细描述):默认参数必须在进行调用的翻译单元中可见。如果在grid_model.h和grid_model.cpp中拆分类,则包含grid_model.h的任何其他.cpp(例如grid_model_test.cpp)将不会知道仅存在于grid_model.cpp中的信息。